Crystal chemistry of layered Pb oxychloride minerals with PbO-related structures: Part II. Crystal structure of vladkrivovichevite, [Pb32O18][Pb4Mn2O]Cl14(BO3)8{middle dot}2H2O

The crystal structure of vladkrivovichevite, a new complex lead oxychloride mineral from the Kombat Mine, Grootfontein, Namibia, has been solved by direct methods and refined to R 1 = 0.048 for 3801 unique observed reflections. The mineral is orthorhombic, Pmmn, a = 12.759(1), b = 27.169(4), c = 11.515(1) Å, and V = 3992.0(9) Å 3 . The structure of vladkrivovichevite belongs to a novel type of layered Pb oxychloride structure. The structure contains 12 symmetrically independent Pb sites. All Pb sites have strongly asymmetric coordination. Two B atoms form slightly distorted BO 3 triangles. One symmetrically independent Mn atom forms five Mn-O bonds and one Mn-Cl bond by forming MnO 5 Cl octahedra. The O1, O2, O10, O11, and O12 atoms are tetrahedrally coordinated by four Pb atoms each, forming OPb 4 oxocentered tetrahedra. The O7 site has a remarkable octahedral coordination, consisting of four Pb and two Mn atoms. The O1Pb 4 , O2Pb 4 , O10Pb 4 , and O11Pb 4 tetrahedra share common edges to produce bands interconnected by O12Pb 4 tetrahedra, forming a [O 18 Pb 32 ] 28+ layer. A O7Pb 4 Mn 2 heterometallic oxocentered octahedron serves as the core of the [OPb 4 Mn 2 Cl 2 (BO 3 ) 8 ] 16- clusters that link to the [O 18 Pb 32 ] 28+ layer via BO 3 triangles. The presence of [OPb 4 Mn 2 Cl 2 (BO 3 ) 8 ] 16- clusters is associated with large cross-like vacancies in the [O 18 Pb 32 ] 28+ layer.